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The following message was posted to: PharmPK
Hi everyone
Hope everyone is well ,
i have a few questions....
is anyone able to explain why good dissolution doesnt necessarily
indicate good bioavailability
i have considered
the effects of food on gastric emptying time,
first pass metabolism in intestine/liver,
and that highly polar drugs do not cross the mucosal membrane in the GI
tract easily to be absorbed ...
can anyone point out other factors involved which I am overlooking?
On another note, does good absorption necessarily indicate good
bioavailability then , and if not , why ?
thanks :)
Linda
Undergraduate Pharmacy Student
Monash University
VIC , Australia
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The following message was posted to: PharmPK
Good dissolution may be an indication for good bioavailability for the
drugs having dissolution rate dependent absorption ( Like low
solubility, high permeability drugs, BCS Class II)and not always as a
common consensus.We observed poor coorelation in some cases specially
for highly variable drugs( HVD)and drugs having very poor
bioavailability.
Even good oral absorption may not be an indicator for good
bioavaliability as many other factors like Presystemic metabolism
(HFPM) are likely to play role.
Regards,
Pradeep Bhadauria
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The following message was posted to: PharmPK
Linda,
Bioavailability (F) is a result of absorption + metabolism. So,
disssolution profile only describes caracteristics of solubility and
some times caracteristics of absorption. (see: Biopharmaceutical
classification).
The two variables together (absortion+metabolism) you can obtain by a
clinical assay of bioavailability. (ex: IV administration x p.o
administration).
A aplication of these points is a bioequivalence studies. Some times a
formulation is equivalent (by dissolution profile) but not
bioequivalent by clinical assay.
I hope this help.
Daniel
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The following message was posted to: PharmPK
dear linda,
please keep in mind that a in vitro dissolution profile does not
necessarily reflect the real solubility of a drug in hydrophilic media.
This is only the case if you would use dissolution media without high
concentrations of artificial surfactants (up to 5% of SDS is used in
our
laboratories). These additives are often applied in dissolution studies
in
order to ensure sink-conditions, which means that the profile only
reflects
the dissolution behaviour of the dosage form (tablet / capsule, etc)
and is
not altered by the solubility of the drug substance itself.
all the best,
Philip
Philip Lienau
Schering AG
Research Pharmacokinetics
Tel.: +49 - 30 - 468 - 18507
Fax: +49 - 30 - 468 - 12238
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